High pressure cylinders are used to supply gas to users in locations that vary from laboratories to a hospital operating room, to remote fields, forests and mines. In addition to gases such as oxygen and nitrogen, cylinders are used to dispense gases that are toxic in nature such as chlorine, bromine, fluorine, arsine, phosphine, diborane, sulphur dioxide and hydrogen sulfide. Cylinders that contain toxic or dangerous gases can on occasion develop small leaks in the valve itself or in the connection between the valve and the cylinder that is used to fill and empty the cylinder. Small leaks can pose a hazard to persons in the vicinity of the cylinders, especially if the cylinders are contained within a room or other confined location. If a cylinder leaks, the leaks often cannot be repaired and thus the cylinders must be returned to the dispenser of the cylinders for correction. The United States Department of Transportation prohibits shipment of leaking cylinders, thus creating the problem of how to contain minor leakage so that the cylinder can be transferred in accord with regulations. Prior to the ever changing and more restrictive rules such cylinders were subjected to onsite disposal or transfer of the product. These operations are conducted by emergency response teams at the location of the problem. However, this means that equipment and personnel must be transported to the scene and measures taken to make the transfer operation safe. Many times the operation of transfer or disposal is conducted under less than ideal conditions and the operations are performed with resources that are not extensive as those normally found in the facilities of the dispenser of the cylinders.
Another option to the dispenser of the cylinders is to contain the entire cylinder inside of a leakproof package for shipment.
Containment caps, e.g. those shown in U.S. Pat. Nos. 3,323,541; 4,478,345; and 4,834,137 have been used in the industry. Cylinders are made in different sizes and in a given size can have different shapes requiring different caps for each class of cylinder. These caps were not interchangeable with other cylinders of a different class (e.g. different size or shape).
One method in use today for handling cylinders is to contain the cylinder into what is called a gas encapsulation unit which can be made leakproof and contain any leakage from the cylinder. The gas encapsulation unit can be vented through a suitable cleanup system or secondary containment system for disposal of the product contained in the leaking cylinder. However, these systems are extremely expensive and generally weigh in excess of 1,000 pounds, so they are not readily portable.